Objective optical system for optical pickup apparatus, optical pickup apparatus, driving apparatus for optical information recording medium, condenser lens and optical path compounding element

Abstract

An objective lens system for an optical pickup apparatus, includes in order from an object side: a first lens group having negative paraxial power P 1 (mm −1 ); and a second lens group having positive paraxial power P 2 (mm −1 ) for converging a light flux emitted from the first lens group on an information recording surface of an optical information recording medium.

1. An objective lens system for an optical pickup apparatus, comprising in order from an object side:
 (a) a first lens group having negative paraxial power P 1  (mm −1 ); and 
 (b) a second lens group having positive paraxial power P 2  (mm −1 ) for converging a light flux emitted from the first lens group on an information recording surface of an optical information recording medium, 
 wherein the negative paraxial power P 1  (mm −1 ) of the first lens group and the positive paraxial power P 2  (mm −1 ) of the second lens group satisfy the following expression,
   0.02<|P 1 /P 2 |<0.30. 
 
 
   
   
     2. The objective lens system of  claim 1 , wherein a numerical aperture on an image side is 0.8 or more. 
   
   
     3. The objective lens system of  claim 1 , wherein a diameter D (mm) of the light flux entering the objective lens system, satisfies the following expression,
   0.7<D<3.0. 
 
   
   
     4. The objective lens system of  claim 1 , wherein the second lens group comprises a single lens. 
   
   
     5. The objective lens system of  claim 4 , wherein the first lens group comprises a single lens. 
   
   
     6. The objective lens system of  claim 5 , wherein a surface on the object side of the first lens group is a convex surface. 
   
   
     7. The objective lens system of  claim 6 , wherein the first lens group is a planoconcave lens, and a flat surface side thereof has a phase structure. 
   
   
     8. The objective lens system of  claim 4 , wherein a focal length f (mm) of the objective lens system and on-axis thickness d 2  (mm) of the second lens group satisfy the following expression,
   0.7≦ d   2 / f≦ 1.4. 
 
   
   
     9. The objective lens system of  claim 4 , wherein a refractive index N d2  of the second lens group for d line satisfies the following expression,
   1.60≦N d2 ≦1.85. 
 
   
   
     10. The objective lens system of  claim 9 , wherein the second lens group is a glass lens. 
   
   
     11. The objective lens system of  claim 4 , wherein a focal length f 2  (mm) of the second lens group and an Abbe's number ν d2  of the second lens for d line satisfy the following expression,
     f   2 /ν d2 ≦0.05. 
 
   
   
     12. The objective lens system of  claim 11 , wherein an Abbe's number ν d1  of the first lens group ford line and the Abbe's number ν d2  of the second lens group for d line satisfy the following expression,
   ν d1 <ν d2 . 
 
   
   
     13. The objective lens system of  claim 1 , wherein a magnification of the objective lens system is substantially zero. 
   
   
     14. The objective lens system of  claim 13 , wherein the magnification m 2  of the second lens group in which spherical aberration correction is optimized, satisfies the following expression,
   −0.15≦ m   2 ≦−0.03. 
 
   
   
     15. The objective lens system of  claim 1 , wherein the objective lens system has a phase structure of a diffractive structure or an optical path difference providing structure, and is capable of converging each of plural light fluxes each having a different wavelength on an information recording surface of each of plural optical information recording media each having different recording density. 
   
   
     16. The objective lens system of  claim 15 , wherein each of plural optical information recording media has a protective layer that is thinner when recording density is higher. 
   
   
     17. The objective lens system of  claim 15 , wherein the first lens group has the phase structure. 
   
   
     18. The objective lens system of  claim 15 , wherein the wavelengths of the plural light fluxes include the first wavelength within a range from 380 to 420 nm and the second wavelength within a range from 630 to 680 nm. 
   
   
     19. The objective lens system of  claim 15 , wherein the wavelengths of the plural light fluxes include the first wavelength within a range from 380 to 420 nm, the second wavelength within a range from 630 to 680 nm, and the third wavelength within a range from 740 to 840 nm. 
   
   
     20. The objective lens system of  claim 1 , wherein the first lens group and the second lens group are held so that relative positions thereof is constant. 
   
   
     21. An optical pickup apparatus comprising:
 (a) a light source; 
 (b) an objective lens system described in  claim 1 ; and 
 (c) a light-receiving system that receives light reflected on the information recording surface of the optical information recording medium, 
 wherein recording and reproducing of information are conducted by converging a light flux emitted from the light source on the information recording surface of the optical information recording medium through the objective lens system. 
 
   
   
     22. A driving apparatus for an optical information recording medium in which the optical pickup apparatus described in  claim 21  is housed, wherein recording and reproducing of information are conducted by the optical pickup apparatus which moves freely in the radial direction of the optical information recording medium for a rotating optical information recording medium.